[Pyode-user] force,mass and geomtransform problem

[Ting L. <dri...@gm...>]

Hello,


I'm learning Pyode now. I'm blocked by the usage of 'geomtransform' and the
mass property.

I intended to make a dumbell in the ode world, composed of two geoms
connecting to one ode body.
When I touch or something hits one of the two balls, the dumbbell should
rotate. (as the center of mass is in the middle)

I made the following program to test if a force acting on a point other than
the center of mass
can make body1 rotate about its center of mass?

I first move the center of mass of body1 to
M1.translate((0.0, 5.0, 0.0))

Then I add a force in x direction at a relative position (0,1,0)
ode_body1.addForceAtRelPos((-100.0,0.0,0.0),(0.0,1.0,0.0))

I expect the sphere1 should move in an arc. But I cannot see the change in
y-axis.
what's wrong here? BTW, can anyone give an example of a dumbbell I described
above
using geomtransform?  Thanks in advance!

#################################################################

import ode


def near_callback(args,geom1,geom2):
    '''callback function for ODE collision detect'''
    #check if two geoms do collide
    contacts = ode.collide(geom1, geom2)

    #get args
    world,contactgroup = args
    for c in contacts:
        c.setBounce(1.0)    #bounceness 0-1
        c.setMu(0)          #friction
        #create contact joint and add it to two bodies
        j = ode.ContactJoint(world,contactgroup,c)
        j.attach(geom1.getBody(),geom2.getBody())
    pass


# Create a ODE world object
ode_world = ode.World()
ode_world.setERP(0.8)
ode_world.setCFM(1E-5)

# Create a space object
ode_space = ode.Space()
# A joint group for the contact joints that are generated whenever
# two bodies collide
ode_contactgroup = ode.JointGroup()



#add ode bodies
ode_body1 = ode.Body(ode_world)
M1 = ode.Mass()
M1.setSphere(1000.0, 1.0)
M1.mass = 1.0
#move the center of gravity
M1.translate((0.0, 5.0, 0.0))
print M1
ode_body1.setMass(M1)

#add geom for body1
geom1 = ode.GeomSphere(ode_space, radius = 1.0)
geom1.setBody(ode_body1)


#add ode bodies
ode_body2 = ode.Body(ode_world)
M2 = ode.Mass()
M2.setSphere(1000.0, 1.0)
M2.mass = 1.0
print M2
ode_body2.setMass(M2)
#add geom for body2
geom2 = ode.GeomSphere(ode_space, radius = 1.0)
geom2.setBody(ode_body2)


#place two bodies along x axis
geom1.setPosition((-1.5, 0.0, 0.0))
geom2.setPosition((1.5, 0.0, 0.0))

#add some force
##ode_body1.addForceAtPos((-100.0,0.0,0.0),(0.0,0.0,0.0))
ode_body1.addForceAtRelPos((-100.0,0.0,0.0),(0.0,1.0,0.0))

#assign a negative velcocity in x-axis to collide with body1
##ode_body2.setLinearVel((-0.5,0,0))
dt=0.0001
while 1:
    print ode_body1.getPosition(),ode_body2.getPosition()

    ode_space.collide((ode_world,ode_contactgroup),near_callback)
    ode_world.step(dt)
    ode_contactgroup.empty()
############################################################################